Heat Wave, Thunderstorms Batter Europe: AIR Analysis

Catastrophe modeling firm AIR Worldwide has analyzed the severe thunderstorms that pummeled western and central Europe, starting on Sunday, June 7. The storms packed “extremely strong and damaging winds, large hail, rampant lightning strikes, and heavy downpours,” AIR said.

They affected a large area as far south as northern Italy and east into Poland, although the worst hit are Germany, France, and Belgium. Severe thunderstorms and high temperatures are affecting other areas as well, including several Central Europe countries, where forest fires sparked by lightning strikes have spread as a result of the intense heat. According to officials, the storms that hit Germany’s North Rhine Westphalia region are the worst in 20 years.

Dr. Yucheng Song, senior scientist at AIR Worldwide, said the “huge supercell thunderstorms” were due to “a cold front that moved into the region from the west, immediately following a severe heat wave. High heat, growing humidity and strong temperature contrast set up the conditions for massive developments of severe weather in the region.”

AIR noted that there have been frequent reports of “hail reaching 3 cm [over an inch] in diameter throughout North Rhine-Westphalia. In Baden-Württemberg an isolated hailstorm produced hailstones reaching a diameter of 7 cm [2.73 inches], while 12 cm hailstones [4.68 inches] were reported in parts of France. Between 2 p.m. Monday and 8 a.m. Tuesday, more than 110,000 lightning bolts were reported in Germany, while over 23,000 were reported in France.

AIR analyzed the damages caused by the storm by country, as follows:Belgium
On June 7, the thunderstorms reached Belgium dropping golf ball-size hail in some areas (including Brussels). Tielt, Sint-Niklaas, Wallonia, and Antwerp were also affected by heavy rain and hail. Lightning and hail caused damage and injuries in Wingene and Knesselare where hailstones reaching 5 cm [1.95 inches] in diameter were reported.

France
On June 8, the storms moved into France, bringing high winds, downpours, lightning, and tennis ball-sized hail (reaching 12 cm in diameter in some areas). Roof damage caused by wind, hail, and flooding was reported in the Val d’Oise and Yvelines areas. In Mormant, roof damage was widespread, affecting homes and businesses.

The worst-affected areas around Paris were Essonne and Seine-et-Marne, east of Paris, where hailstones as large as 10 cm [3.9 inches] were reported. Other affected areas of France included Normandy and Dordogne. Vineyards across France sustained damage from hail and high winds, including 1,000 hectares in Bordeaux and 680 hectares near Blaignan. In Charente, winds reached 130 km/h [80.6 mph] and both the city and surrounding vineyards were battered by hail and rain. After a brief respite Monday morning, additional storms returned to France and persisted until Tuesday morning.

Germany
The worst damage occurred in Germany’s most populous state, North Rhine-Westphalia, which was hit Monday evening. Heavy winds at Düsseldorf’s airport, Germany’s third largest, reached 150 km/h [93 mph] on Tuesday night, causing air traffic delays due to grounded planes. Heavy winds toppled trees and caused further damage in Cologne and Essen. The thunderstorms also caused significant crop damage in Germany, especially in areas west of Kassel.

The storms continued eastward into Lower Saxony where warnings were issued for Hanover and Bremen. In several cities of Lower Saxony, roof fires were ignited by lightning. Damage and disruption of public transportation occurred in other states including Mecklenburg-Vorpommen, where flooding was reported in several areas, including Rostock, where 20 mm of rain fell within a short time period. By Tuesday evening, storms were still causing significant damage in Hessen, affecting Kassel, Göttingen, and other cities. According to Deutsche Bahn officials, damage in the Rhine-Ruhr region is worse than was seen in 2007 when the area was struck by winter storm Kyrill.

According to AIR, “residential building stock in Europe is predominantly of masonry construction. Mid-rise residential buildings generally have exterior non-load bearing walls made of masonry although they may have light-gauge steel stud walls or concrete panels. Reinforced concrete can also be found in most European countries, especially for mid-rise apartment buildings, while steel is used for high-rise apartment and condominium buildings that are usually located in large urban areas. For commercial exposures, the construction type is approximately 50 percent masonry with the remaining construction split between steel frame and reinforced concrete.”

Yörn Tatge, managing director of AIR Worldwide GmbH, explained: “When built areas are subjected to the level of winds reported here, most of the damage comes from toppled trees and broken branches, as trees are in full leaf. Strong winds can also damage cladding. In Europe, rooftops often experience tile damage, with many tiles broken and blown off due to wind force. Uplift of the roof edges allows the wind to penetrate underneath the roof membrane, which raises the pressure and can remove the roof covering.

“At very high wind speeds, the integrity of the entire structure can be compromised, particularly in cases where the roof provides the lateral stability by supporting the tops of the building’s walls. Hail and flying debris can cause extensive damage, particularly to autos and greenhouses.”

“In Europe, cellars are common in both residential and commercial buildings, increasing the vulnerability to flood damage. The presence of a cellar also increases the risk for contents damage, particularly in the case of heavily-used cellars that enclose recreational rooms, bedrooms, or home offices. Some homes may have entire apartments located in the cellar as well. However, heavily-used cellars usually have better flood defense mechanisms than unfinished ones. The contents in the lower stories and cellars can vary widely depending on the occupancy class.”

Dr. Song concluded: “Recent thunderstorms have brought cooler air into the northern and central parts of Europe. However, temperatures in the Czech Republic are still in the high 20s °C (80s – 90s °F). More thunderstorms are expected to begin in the afternoon of Thursday June 12, and will bring additional rain and hail to the region.”